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NASA NTRS1973

Electron-proton spectrometer

An electron-proton spectrometer was designed to measure the geomagnetically trapped radiation in a geostationary orbit at 6.6 earth radii in the outer radiation belt. This instrument is to be flown on the Applications Technology Satellite-F (ATS-F). The electron-proton spectrometer consists of two permanent magnet surface barrier detector arrays and associated electronics capable of selecting and detecting electrons in three energy ranges: (1) 30-50 keV, (2) 150-200 keV, and (3) 500 keV and protons in three energy ranges. The electron-proton spectrometer has the capability of measuring the fluxes of electrons and protons in various directions with respect to the magnetic field lines running through the satellite. One magnet detector array system is implemented to scan between EME north and south through west, sampling the directional flux in 15 steps. The other magnet-detector array system is fixed looking toward EME east.

Winckler, J. R.↗
NASA NTRS1973

Propagation anisotropies of solar flare protons and electrons at low energies in interplanetary space.

Flux anisotropies in interplanetary space were investigated for protons with E greater than 0.66 MeV and electrons with E greater than 400 keV. Data were taken from the University of Chicago charged-particle telescope aboard the deep-space probe Pioneer 7 and from the Goddard Space Flight Center magnetometer aboard the same spacecraft. Flux anisotropies lying to the east of the average interplanetary magnetic field direction were first reported by McCracken et al. (1971), late in a solar particle event, for proton energies greater than 7.5 MeV. This work extends this investigation to much lower proton energies, studies the proton and electron anisotropies during both early and late phases of a particle event, and makes use of detailed magnetic field data. The investigation consists of two parts, a study of many periods taken at random during solar events, for both protons and electrons, and a detailed analysis of one period, early in an event, during which the magnetic field was near the solar direction.

Pyle, K. R.↗
NASA NTRS1974

Stably trapped proton fluxes in the Jovian magnetosphere

A model of the energetic proton fluxes in the Jovian magnetosphere is constructed based on the inward radial diffusion of protons from the solar wind and the plasma turbulent precipitation loss of protons from the radiation belts. Outside 12 Jovian radii the proton fluxes follow a loss-free radial diffusion profile. Inside 12 Jovian radii the proton fluxes should be near the stably trapped limit flux set by convective marginal stability to the electromagnetic ion cyclotron wave and the quasi-electrostatic ion loss-cone wave.

Coroniti, F. V.↗
NASA NTRS1974

Anisotropic proton instability magnetospheric /APIM/ hiss - An introduction

Plasmaspheric hiss is broadband ELF noise between 100 and 2000 Hz generally occurring inside the plasmasphere. It is proposed that some plasmaspheric ELF hiss is generated by ring current protons. The mechanism by which waves are generated is the anisotropic proton instability magnetospheric (APIM) hiss mechanism. APIM hiss (with a frequency close to the lower hybrid resonance frequency) is a loss-cone, flute instability arising from proton velocity space anisotropies. The energy driving the waves comes from the free energy of the 'inverted population' of the proton loss-cone distribution. The APIM hiss mechanism predicts the bandwidth, center frequency, source location, and wave normal angle of some types of plasmaspheric hiss. APIM hiss is suggested as a possible additional loss mechanism for ring current protons.

Parady, B. K.↗
NASA NTRS1975

The upstream escape of energized solar wind protons from the bow shock

The paper analyzes the geometry of escape from the bow shock for solar wind protons in order to determine under what conditions a proton reflected from the bow shock can escape upstream or not. Some numerical examples show that protons with rather high energies and pitch angles can escape the shock at only marginally quasi-parallel field orientations, even if they have quite moderate speeds parallel to B. This does not provide evidence that such high energy protons are produced at the bow shock, but does show that such protons can escape upstream with the characteristics observed by Lin et al. (1974). It is also possible that some particles will encounter the shock two or more times, their total energy compounding until it reaches a high level.-

Greenstadt, E. W.↗
NASA NTRS1976

Fluxes of protons above 50 keV and electrons above 30 keV at approximately 35 earth radii. I - Velocity anisotropies and plasma flow in the magnetotail. II Morphology and flow patterns in the magnetotail

Imp-7 data were used to study the morphology and flow patterns of energetic proton and electron events in the magnetotail and magnetosheath at 35 earth radii. The patterns are deduced from the probability of occurrence and the spatial distribution of the events. The distribution of 50 to 200 keV proton and 30 to 90 keV electron fluxes shows that in the magnetotail (i.e., inside the magnetopause) the proton and electron events occur primarily in the plasma sheet region within plus or minus 10 earth radii of the neutral sheet; fluxes of 50- to 200-keV protons are also found in the magnetosheath, along with occasional fluxes of 30- to 90-keV electrons; the plasma sheet is well defined (at 35 earth radii) by both the proton and electron probabilities; the frequency of the electron events in the magnetotail shows a positive correlation with the geomagnetic Kp index in the dawn and dusk sectors.

Roelof, E. C.↗
NASA NTRS1976

Lyman-alpha emission from nonthermal proton beams

Nonthermal fast protons penetrating an atmosphere containing neutral hydrogen will produce some nonthermal fast neutrals which will radiate Doppler-shifted photons. The hydrogen line profiles observed from such an atmosphere will thus have nonthermal, partially polarized wings that contain information on the flux, energy spectrum, and direction of the incident proton beam. This paper develops the theory of this effect and applies it to proton beams from impulsive solar flares impacting on the sun's atmosphere. Calculations of the L-alpha profile from the region of impact have been made for the Vernazza-Avrett-Loeser solar atmosphere assuming proton energy fluxes and power-law spectra similar to those inferred for the electron beams believed responsible for hard X-ray bursts. The resulting profiles show that the effect should be detectable and that it could serve as a diagnostic for flare protons near their place of origin on the sun.

Orrall, F. Q.↗
NASA NTRS1979

Low energy proton radiation damage to (AlGa)As-GaAs solar cells

Twenty-seven 2 times 2 sq cm (AlGa)As-GaAs solar cells were fabricated and subjected to 50 keV, 100 keV, and 290 keV of proton irradiation along with eighteen high efficiency silicon solar cells. The results of the study further corroborate the advantages for space missions offered by GaAs cells over state of the art silicon cells. Thus, even though the GaAs cells showed greater degradation when irradiated by protons with energy less than 5 MeV, the solar cells were normally protected from these protons by the glass covers used in space arrays. The GaAs cells also offered superior end of life power capability compared with silicon. The change in the open circuit voltage, short circuit current, spectral response, and dark 1-5 characteristics after irradiation at each proton energy and fluence were found to be consistent with the explanation of the effect of the protons. Also dark 1-5 characteristics showed that a new recombination center dominates the current transport mechanism after irradiation.

Loo, R.↗
NASA NTRS1978

Effects of proton irradiation on a gas phase in which condensation takes place. I Negative Mg-26 anomalies and Al-26

In the present paper, isotopic effects in magnesium generated in a proton-irradiated gas phase are examined, taking only (p,n), (p,d), and (p, alpha) reactions in magnesium, aluminum, and silicon into consideration. In the presence of proton radiation, the three elements are 'removed' from the gas phase by condensation. It is required that a value of Al-26/Al-27 greater than 6 times 10 to the -5th must be reached, consistent with the value deduced by Lee Papanastassiou, and Wasserburg (1976) from their studies of the Allende meteorite. The calculations show that fast aluminum condensation reduces the required proton fluence substantially, that a significant fraction of aluminum remains uncondensed when the above value of the Al-26/Al-27 ratio is reached, that a detectable MG-24 excess is very likely to occur, that detectable negative MG-28 anomalies can be generated, and that proton fluxes and irradiation times can be varied simultaneously, and over a wide range of values, without significant changes in the required proton fluence.

Heymann, D.↗
NASA NTRS1980

Sources of high-energy protons in Saturn's magnetosphere

The passage of Pioneer 11 through Saturn's magnetosphere revealed an especially intense region of high-energy particle fluxes that places unique constraints on models for sources of high-energy protons in the innermost radiation zones. Of special interest is the flux of protons with energies above 35 MeV which was measured with a fission cell in the innermost magnetosphere between the A ring and the orbit of Mimas. The negative phase space density gradients derived from the proton and electron observations in this region imply that steady-state inward diffusion from the outer magnetosphere is not an adequate source for these high-energy protons. In the present paper, the nature of the Crand source at Saturn is examined, and its significance for injection of high-energy protons into the region inside L = 4 is estimated.

Cooper, J. F.↗
NASA NTRS1980

Deep-level defects and recombination parameters in proton irradiated AlGaAs-GaAs solar cells

The deep-level defects produced in high efficiency AlGaAs-GaAs solar cells by proton energies of 50, 100, 200, and 290 keV are investigated. Proton fluences were from 10 to the 10th to 10 to the 13th p/sq cm. The results show that the diode ideality factor varies between 1.9 and 2.1, indicating that the dominant current component is due to the recombination of electron-hole pairs via deep-level traps in the junction space charge region of these diodes. The recombination current increases with increasing proton fluence and proton energy. The reduction of open circuit voltage, short circuit current, and conversion efficiency in the irradiated cells relates directly to the density of the deep-level defects induced by proton irradiation.

Li, S. S.↗
NASA NTRS1982

A model for proton-irradiated GaAs solar cells

A simple model for proton radiation damage in GaAs heteroface solar cells is developed. The model includes the effects of spatial nonuniformity of low energy proton damage. Agreement between the model and experimental proton damage data for GaAs heteroface solar cells is satisfactory. An extension of the model to include angular isotropy, as is appropriate for protons in space, is shown to result in significantly less cell damage than for normal proton incidence.

Wilson, J. W.↗
NASA NTRS1981

Study of radiation induced deep-level defects and annealing effects in the proton irradiated AlGaAs-GaAs solar cells

The radiation induced deep-level defects and the recombination parameters in the proton irradiated AlGaAs-GaAs p-n junction solar cells were investigated over a wide range of proton energies (from 50 KeV to 10 MeV) and proton fluences (from 10 to the 10th to 10 to the 13th P/sq cm), using DLTS, I-V, C-V, and SEM-EMIC measurement techniques. The measurements were used to determine the defect and recombination parameters such as defect density and energy level, carrier lifetimes, and the hole diffusion lengths in the GaAs LPE layers. Results show that a good correlation was obtained between the measured defect parameters and the dark recombination current as well as the performance parameters of the solar cells. The most damages to the cell were produced by the 200 KeV protons. In addition, the effects of low temperatures (200 to 400 C) thermal annealing on the deep-level defects and the dark current of the 200 KeV proton irradiated samples were examined.

Li, S. S.↗
NASA NTRS1983

Nuclear cascades in Saturn's rings - Cosmic ray albedo neutron decay and origins of trapped protons in the inner magnetosphere

The nearly equatorial trajectory of the Pioneer 11 spacecraft through Saturn's high energy proton radiation belts and under the main A-B-C rings provided a unique opportunity to study the radial dependence of the greater than 30 MeV proton intensities in the belts in terms of models for secondary nucleon production by cosmic ray interactions in the rings, in situ proton injection in the radiation belts by neutron beta decay, magnetospheric diffusion, and absorption by planetary rings and satellites. Maximum trapped proton intensities measured by Pioneer 11 in the radiation belts are compared with calculated intensities and found consistent with trapping times of roughly 40 years and a radial diffusion coefficient of about 10 to the -15th L to the 9th R sub s squared/s. Differential energy spectra proportional to E to the -2 estimated from integral measurements of trapped photons with E greater than 100 MeV are consistent with the beta decay model, but an inferred turndown of the spectra toward lower energies and reported integral proton anisotropies of a specified form both indicate the need for more realistic calculations of the neutron source from the rings and the radiation belt loss processes.

Cooper, J. F.↗
NASA NTRS1985

On the detectability of key-MeV solar protons through their nonthermal Lyman-alpha emission

The intensity and timescale of nonthermal Doppler-shifted hydrogen L alpha photon emission as diagnostics of 10 keV to 10 MeV protons bombarding the solar chromosphere during flares are investigated. The steady-state excitation and ionization balance of the proton beam are determined, taking into account all important atomic interactions with the ambient chromosphere. For a proton energy flux comparable to the electron energy flux commonly inferred for large flares, L alpha wing intensities orders of magnitude larger than observed nonflaring values were found. Investigation of timescales for ionization and charge exchange leads researchers to conclude that over a wide range of values of mean proton energy and beam parameters, Doppler-shifted nonthermal L alpha emission is a useful observational diagnostic of the presence of 10 keV to 10 MeV superthermal proton beams in the solar flare chromosphere.

Canfield, R. C.↗
NASA NTRS1986

Beam-induced pressure gradients in the early phase of proton-heated solar flares

The pressure gradient induced in a coronal loop by proton beam momentum deposition is calculated and compared with the thermal pressure gradient arising from nonuniform deposition of beam energy; it is assumed that the transfer of momentum and energy from beam to target occurs via the Coulomb interaciton. Results are presented for both a low mean energy and a high mean energy proton beam injected at the loop apex and characterized by a power-law energy spectrum. The present treatment takes account of the breakdown of the cold target approximation for the low-energy proton beam in the corona, where the thermal speed of target electrons exceeds the beam speed. It is found that proton beam momentum deposition plays a potentially significant role in flare dynamics only in the low mean energy case and only in the corona, where it may dominate the acceleration of target material for as long as several tens of seconds. This conclusion suggest that the presence of low-energy nonthermal protons may be inferred from velocity-sensitive coronal observations in the early impulsive phase.

Tamres, David H.↗
NASA NTRS1987

Proton and oxygen plasmas at Uranus

Despite the presence of several large, ice moons within the Uranian magnetosphere, the Voyager 2 spacecraft did not detect any heavy ion plasma. This paper estimates the heavy ion density that would be consistent with a heavy neutral torus formed by photosputtering, charged particle sputtering, and micrometeoroid impact vaporization of icy surfaces on the moons, taking into account the large 60 deg angle between the satellite orbit plane and the magnetic equator. The expected heavy ion density is unobservably small. The observed proton plasma of the inner magnetosphere can be maintained by ionization of the atomic hydrogen corona and by the ionospheric proton source driven by photoelectron escape, for a plasma residence time of about 30 days. These two proton sources are comparable near L = 5. The same 30-day residence time for energetic protons implies an upper limit of 0.00001 on the fraction of incident solar wind protons that enter the magnetosphere and penetrate to within L less than 6 while conserving their first adiabatic invariants.

Cheng, Andrew F.↗
NASA NTRS1988

Effect of solar proton events in 1978 and 1979 on the odd nitrogen abundance in the middle atmosphere

Daily average solar proton flux data for 1978 and 1979 are used in a proton energy degradation scheme to derive ion pair production rates and atomic nitrogen production rates. The latter are computed in a form suitable for inclusion in an atmopheric, two-dimensional, time-dependent photochemical model. Odd nitrogen distributions are computed from the model, including atomic nitrogen production from solar protons, and are compared with baseline distributions. The comparisons show that the average effect of the solar protons in 1978 and 1979 was to cause changes in odd nitrogen only above 10 mbar and at latitudes only above about 50 deg in both hemispheres. The influence of the solar proton-produced odd nitrogen on the local abundance of odd nitrogen depends primarily on the background odd nitrogen abundance as well as the altitude and season.

Jackman, Charles H.↗